The invention relates to multiframe alignment and its consequent actions in general and especially to a multiframe alignment for tandem connection trails at Non Intrusive Monitoring (NIM) Trail Termination (TT) sink functions and for TT sink functions in a Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) system.
The problem addressed with this invention typically arises in Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) systems in case of protection switches within a Tandem Connection Trail. For a better understanding of SDH and SONET systems, reference is made to xe2x80x9cUnderstanding of SONET/SDHxe2x80x9d, ISBN 0-9650448-2-3, Andan Publisher, New Jersey.
In the before-mentioned network system a tandem connection is intended to provide an administrative monitoring domain which is operating independent of the end to end path. Rules for the establishment of a tandem connection trail are defined in ETSI EN 300 417-4-1 and ITU-T G.783.
The operation and also the establishment of a tandem connection trail shall influence the rest of the network system as less as possible. Under certain circumstances (i.e. if switching actions are performed within a tandem connection trail), current Tandem Connection Monitoring (TCM) implementations according to the current versions of the standards unnecessarily enlarge signal disturbances.
Accordingly, there is a need to reduce the influence of protection switches within a tandem connection trail in a Synchronous Digital Hierarchy (SDH) or in a Synchronous Optical Network (SONET) System by avoiding enlargements of signal disturbances caused by protection switches.
An enhanced multiframe processing method and synchronous hierarchic network system optimized for the application with transmission protection schemes achieves the invention.
In current implementations the loss of the aligned signal reception resulting in an out of multiframe (OOM) signal transmission state subsequent to an interruption, distortion or switching operation of the signal transmission path leads to the detection of a Loss of Tandem Connection defect(dLTC) accompanied with an insertion of all ones as consequent action for the dLTC defect. This all ones insertion results in an undue interruption of the signal. The method of this invention avoids the immediate reaction on the OOM state by delaying the dLTC detection in the OOM state for a predefined time interval.